<template>
	<ul class="list">
		<li class="item" 
			v-for="item of letters" 
			:key="item"
			:ref="item"
			@click="handleLetterClick"
			@touchstart="handleTouchStart"
			@touchmove="handleTouchMove"
			@touchend="handleTouchEnd"
			>
			{{item}}
		</li>
	</ul>
</template>

<script>
	export default {
		name:'CityAlphabet',
		props:{
			cities:Object
		},
		computed: {
			letters () {
				const letters = []
				for(let i in this.cities) {
					letters.push(i)
				}
				return letters
			}
		},
		data() {
			return {
				touchStatus:false,
				startY: 0,
				timer: null
			}
		},
		updata () {
			this.startY =  this.$refs["A"][0].offsetTop
		},
		methods: {
			handleLetterClick (e) {
				this.$emit('change',e.target.innerText)
			},
			handleTouchStart () {
				this.touchStatus = true
			},
			handleTouchMove(e) {
				if(this.touchStatus) {
					if(this.timer) {
						clearTimeout(this.timer)
					}
					this.timer = setTimeout(()=>{
						const touchY = e.touches[0].clientY - 79
						const index = Math.floor((touchY - this.startY)/20)
						if(index >=0 && index <= this.letters.length){
							this.$emit('change',this.letters[index])
						}
					},16)							
				}
			},
			handleTouchEnd () {
				this.touchStatus = false
			}
		}
	}
</script>

<style lang="stylus" scoped>
	@import '~styles/varibles.style'
	.list
		display: flex
		flex-direction: column
		justify-content: center
		position:absolute
		top:1.58rem
		right:0
		bottom:0
		width:.4rem	
		.item
			text-align:center
			line-height:.4rem
			color:$bgColor
</style>